What are the basic requirements of a Laser?

Basic requirement of a Laser are as follows:

1. Active Medium:

Active basic medium is needed to start the laser action. There the atomic or molecular transitions take place to the laser action. As solid, gas, liquid, dye or semiconductor may be utilized as active medium

2. Pumping System

The basic system is needed to attain the pumping action into the active medium

3. Optical Resonator

This system is made by a pair of reflecting surfaces facing each other wherein one is totally reflecting and the other is partially reflecting. Such mirrors are kept onto the both sides of active medium throughout laser action are bounced back and forth among these two reflecting surfaces. That reflection process induces growingly stimulated transition leading laser action.